Related subject matter is disclosed in the concurrently filed application entitled xe2x80x9cMULTIPLE WAVELENGTH LASER HAVING A REDUCED NUMBER OF WAVELENGTH CONTROLSxe2x80x9d by the inventors, C. R. Doerr., C. P. Dragone, and A. M. Glass, which is assigned to the same Assignee as the present application.
The present invention relates to a Waveguide Grating Router (WGR) and, more particularly, to a WGR having a large number N of input and output ports.
Large Nxc3x97N waveguide grating routers (WGR) represent an excellent solution for providing large optical cross-connects: They are fully passive elements and they can provide strictly non-blocking connections for a set of N optical channels. [1-5]. (Note in this specification, a reference to another document is designated by a number in brackets to identify its location in a list of references found in the Appendix)
However, due to the intrinsic diffraction characteristics of the grating, restrictions limit the size of a Nxc3x97N WGR. Additional and even more severe limitations arise if the WGR is designed to cross-connect channels which are equally spaced in frequency [4,6] as opposed to being equally spaced in wavelength.
Because the number of wavelengths being used in an optical system is constantly increasing, there is a continuing need to increase the size of the Nxc3x97N WGRs used as optical cross-connects.
In accordance with the present invention, we have recognized that because of the intrinsic diffraction characteristics of the grating, restrictions in the size of N generally happens when N approaches the diffraction order m at which the grating operates. We have developed a technique for maximizing N in a Nxc3x97N WGR device for channels equally spaced either in frequency or in wavelength.
For the wavelength case, N is increased by appropriate changes in the spacing of the output ports of the WGR and/or by slightly correcting the channels wavelengths.
More particularly, the N in a Nxc3x97N WGR is maximized for input signals including N equally spaced wavelengths by using an output coupler having N output ports that are shifted from their original uniformly spaced position. In another embodiment used with input signals having N wavelengths or frequencies, the N in a Nxc3x97N WGR is maximized by using N wavelengths or frequencies that are not equally spaced. In yet another embodiment, used with input signals having N wavelengths or frequencies, the N in a Nxc3x97N WGR is maximized by using an output coupler having N output ports that are spaced to maximize the weakest signal transmission coefficient of at least one of the N wavelengths or frequencies from any of the N input ports.